VARIABILITY OF ACOUSTIC TURBIDITY IN ECKERNFORDE BAY (SOUTHWEST BALTIC SEA) RELATED TO THE ANNUAL TEMPERATURE CYCLE

The sediments of Eckernforde Bay (southwest Baltic Sea) are known for their high contents of gas. It causes acoustic turbidity, i.e., the ma sking of sedimentary horizons by absorption and scattering of seismic energy due to free gas bubbles, also known as ''basin effect''. Repeat ed surveys with side-scan sonar and subbottom profiler along coinciden t profiles gave new insight into the variability of the acoustic turbi dity. For the first time it is evidenced that its depth varies by seve ral decimeters with an annual cycle. We explain this by the temperatur e-dependent solubility of methane. The depth of the acoustic turbidity , however, does not vary in phase with the annual surface temperature cycle. The delay is an effect of the poor heat conductivity of the ove rlying water and sediment.